1. Field of the Invention
This invention relates to heat activated links for use in automatically actuated equipment forming a part of fire fighting systems, and in particular to a resettable heat activated fire link for use with such systems.
2.Prior Art
The present invention generally relates to releasing devices, and more particularly, releasing devices employing bimetallic elements. These releasing devices are conventionally useful to actuate various fire protection equipment in response to increases in heat in the vicinity of the device.
Conventionally, fusible or meltable releasing devices have been used. These fusible or meltable releasing devices included such things as fusible links and cables which ar held under tension in normal conditions and which are actuated by the melting of the link and the resulting break in the cable. However once activated, these links could not be reset. Thus it was not convenient or economical to test systems using these links.
It is also known in the art to use bimetallic links such as those taught in U.S. Pat. No. 3,889,314 entitled "Heat Actuated Link" and U.S. Pat. No. 3,725,972 entitled "Fire Link and Method of Actuating Link". The bimetallic links taught in these patents included a releasing element having a bimetallic strip attached thereto. The bimetallic strip and the releasing element acted cooperatively to engage a pawl having an aperture. The aperture was engaged by a pin coupled to the bimetallic element in the normal unactuated position of the link and released as the tip of pin coupled to the bimetallic element separated from a mounting or a striker portion of the link to release the pawl. These bimetallic links have conventionally been installed by attaching a cable to either the pawl, a mounting element attached to the bimetallic element, or both in a manner similar to that used for the fusible or meltable links described above.
These bimetallic links have exhibited certain advantages compared with the prior art fusible links in that following a return to normal temperatures, the link may be reset simply by reinserting the pawl into the remaining link assembly by resiliently moving the pin portion of the link. However, these links were somewhat difficult and expensive to construct because they were formed of several parts requiring assembly and fastening as well as the inconvenience of maintaining an inventory of many small parts. In addition to being more expensive and more inconvenient, the number of parts increased the risk of failure of the links.
These parts which were assembled included at least a base portion, a pin and a washer associated with the pin. Additionally, these links included further parts such as the bimetallic element and an insulating material between the bimetallic material and the base portion. Rivets were often required to attach the bimetallic element to the base causing additional construction expense and additional opportunity for failure. Finally, a pawl was often required for releasable engagement with the link.
In addition to the number of parts, another problem with prior art heat actuated links wa their size. When trying to miniaturize heat actuated links a limiting factor is the length of the bimetallic element. The length of the element is a limiting factor because the temperature at which a link is activated depends upon the length of the bimetallic strip element. In order to provide a new link actuated at the same temperature as a prior art link, the new link was required to have substantially the same length bimetallic element in order to operate at the same temperature range. Therefore the size of the new link has approximately the same length bimetallic element.
Therefore it is an object of the present invention to provide a heat actuated link avoiding the need for many individual parts requiring assembly and fastening a in the prior art heat actuated links.
Additionally, it is an object of the present invention to provide a heat actuated link wherein a link may operate at the same temperature as a prior art link while having a more compact size than the size of a prior art link.